Communication system in digital television

ABSTRACT

A VSB communication system or transmitter for processing supplemental data packets with MPEG-II data packets includes a VSB supplemental data processor and a VSB transmission system. The VSB supplemental data processor includes a Reed-Solomon coder for coding the supplemental data to be transmitted, a repetition coder for inserting repetion data to an intereaved supplemental data for generating a predefined sequence, a header inserter for inserting an MPEG header to the supplemental data having the repetion code inserted therein, a multiplexer for multiplexing an MPEG data coded with the supplemental data having the MPEG header added thereto in a preset multiplexing ratio and units. The output of the multiplexer is provided to an 8T-VSB transmission system for modulating a data field from the multiplexer and transmitting the modulated data field to a VSB reception system.

CROSS REFERENCE TO RELATED ART

[0001] This application claims the benefit of Korean Patent ApplicationNo. 2001-22200, filed on Apr. 25, 2001, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a digital televisiontransmission system, and more particularly, to a 8T-VSB (VestigialSideband) transmission system for transmitting supplemental data inaddition to MPEG data and to a signal format for the VSB transmissionsystem.

[0004] 2. Description of the Related Art

[0005] The United States of America has employed ATSC 8T-VSB (8Trellis-Vestigial Sideband) as a standard since 1995, and has beenbroadcasting in the ATSC 8T-VSB since the later half of 1998. SouthKorea also has employed the ATSC 8T-VSB as a standard. South Koreastarted test broadcasting in May 1995, and has since August 2000 put inplace a regular test broadcasting system. The advancement of technologyallows the transmission of digital television (DTV) in the same 6 MHzbandwidth currently used by NTSC.

[0006]FIG. 1 illustrates a block diagram of a related art ASTC 8T-VSBtransmission system (“VSB transmission system”). The VSB transmissionsystem 16 generally comprises a data randomizer 1, Reed-Solomon coder 2,data interleaver 3, Trellis coder 4, multiplexer 5, pilot inserter 6,VSB modulator 7 and RF converter 8.

[0007] Referring to FIG. 1, there is a data randomizer 1 for receivingand making random MPEG data (video, audio and ancillary data). The datarandomizer 1 receives the MPEG-II data output from an MPEG-II encoder.Although not shown in FIG. 1, the MPEG-II encoder takes baseband digitalvideo and performs bit rate compression using the techniques of discretecosine transform, run length coding, and bi-directional motionprediction. The MPEG-II encoder then multiplexes this compressed datatogether with pre-coded audio and any ancillary data that will betransmitted. The result is a stream of compressed MPEG-II data packetswith a data frequency of only 19.39 Mbit/Sec. The MPEG-II encoderoutputs such data to the data randomizer in serial form. MPEG-II packetsare 188 bytes in length with the first byte in each packet always beingthe sync or header byte. The MPEG-II sync byte is then discarded. Thesync byte will ultimately be replaced by the ATSC segment sync in alater stage of processing.

[0008] In the VSB transmission system 16, the 8-VSB bit stream shouldhave a random, noiselike signal. The reason being that the transmittedsignal frequency response must have a flat noise-like spectrum in orderto use the allotted 6 MHz channel space with maximum efficiency. Randomdata minimizes interference into analog NTSC. In the data randomizer 1,each byte value is changed according to known pattern of pseudo-randomnumber generation. This process is reversed in the VSB receiver in orderto recover the proper data values.

[0009] The Reed-Solomon coder 2 of the VSB transmission system 16 isused for subjecting the output data of the data randomizer 1 toReed-Solomon coding and adding a 20 byte parity code to the output data.Reed Solomon encoding is a type of forward error correction schemeapplied to the incoming data stream. Forward error correction is used tocorrect bit errors that occur during transmission due to signal fades,noise, etc. Various types of techniques may be used as the forward errorcorrection process.

[0010] The Reed-Solomon coder 2 takes all 187 bytes of an incomingMPEG-II data packet (the sync or header byte has been removed from 188bytes) and mathematically manipulates them as a block to create adigital sketch of the block contents. This “sketch” occupies 20additional bytes which are added at the tail end of the original 187byte packet. These 20 bytes are known as Reed-Solomon parity bytes. The20 Reed-Solomon parity bytes for every data packet add redundancy forforward error correction of up to 10 byte errors/packet. SinceReed-Solomon decoders correct byte errors, and bytes can have anywherefrom 1 to 8 bit errors within them, a significant amount of errorcorrection can be accomplished in the VSB receiver. The output of theReed-Solomon coder 2 is 207 bytes (187 plus 20 parity bytes).

[0011] The VSB receiver will compare the received 187 byte block to the20 parity bytes in order to determine the validity of the recovereddata. If errors are detected, the receiver can use the parity bytes tolocate the exact location of the errors, modify the corrupted bytes, andreconstruct the original information.

[0012] The data interleaver 3 interleaves the output data of theReed-Solomon coder 2. in particular, the data interleaver 3 mixes thesequential order of the data packet and disperses or delays the MPEG-IIpacket throughout time. The data interleaver 3 then reassembles new datapackets incorporating small sections from many different MPEG-II(pre-interleaved) packets. The reassembled packets are 207 bytes each.

[0013] The purpose of the data interleaver 3 is to prevent losing of oneor more packets due to noise or other harmful transmission environment.By interleaving data into many different packets, even if one packet iscompletely lost, the original packet may be substantially recovered frominformation contained in other packets.

[0014] The VSB transmission system 16 also has a trellis coder 4 forconverting the output data of the data interleaver 3 from byte form intosymbol form and for subjecting it to trellis coding. Trellis coding isanother form of forward error correction. Unlike Reed-Solomon coding,which treated the entire MPEG-II packet simultaneously as a block,trellis coding is an evolving code that tracks the progressing stream ofbits as it develops through time.

[0015] The trellis coder 4 adds additional redundancy to the signal inthe form of more (than four data levels, creating the multilevel (8)data symbols for transmission. For trellis coding, each 8-bit byte issplit up into a stream of four, 2-bit words. In the trellis coder 4,each 2-bit input word is compared to the past history of previous 2-bitwords. A 3-bit binary code is mathematically generated to describe thetransition from the previous 2-bit word to the current one. These 3-bitcodes are substituted for the original 2-bit words and transmitted asthe eight level symbols of 8-VSB. For every two bits that enter thetrellis coder 4, three bits come out.

[0016] The trellis decoder in the VSB receiver uses the received 3-bittransition codes to reconstruct the evolution of the data stream fromone 2-bit word to the next. In this way, the trellis coder follows a“trail” as the signal moves from one word to the next through time. Thepower of trellis coding lies in its ability to track a signal's historythrough time and discard potentially faulty information (errors) basedon a signal's past and future behavior.

[0017] A multiplexer 5 is used for multiplexing a symbol stream from thetrellis coder 4 and synchronizing signals. The segment and the fieldsynchronizing signals provide information to the VSB receiver toaccurately locate and demodulate the transmitted RF signal. The segmentand the field synchronizing signals are inserted after the randomizationand error coding stages so as not to destroy the fixed time andamplitude relationships that these signals must possess to be effective.The multiplexer 5 provides the output from the trellis coder 4 and thesegment and the field synchronizing signals in a time division manner.

[0018] An output packet of the data interleaver 3 comprises the 207bytes of an interleaved data packet. After trellis coding, the 207 bytesegment is stretched out into a baseband stream of 828 eight levelsymbols. The segment synchronizing signal is a four symbol pulse that isadded to the front of each data segment and replaces the missing firstbyte (packet sync byte) of the original MPEG-II data packet. The segmentsynchronizing signal appears once every 832 symbols and always takes theform of a positive-negative-positive pulse swinging between the +5 and−5 signal levels.

[0019] The field synchronizing signal is an entire data segment that isrepeated once per field. The field synchronizing signal has a known datasymbol pattern of positive-negative pulses and is used by the receiverto eliminate signal ghosts caused by poor reception.

[0020] The VSB transmission system 16 also has the pilot inserter 6 forinserting pilot signals into the symbol stream from the multiplexer 5.Similar to the synchronizing signals described above, the the pilotsignal is inserted after the randomization and error coding stages so asnot to destroy the fixed time and amplitude relationships that thesesignals must possess to be effective.

[0021] Before the data is modulated, a small DC shift is applied to the8T-VSB baseband signal. This causes a small residual carrier to appearat the zero frequency point of the resulting modulated spectrum. This isthe pilot signal provided by the pilot inserter 6. This gives the RF PLLcircuits in the VSB receiver something to lock onto that is independentof the data being transmitted.

[0022] After the pilot signal has been inserted by the pilot inserter 6,the output is subjected to a VSB modulator 7. The VSB modulator 7modulates the symbol stream from the pilot inserter 6 into an 8 VSBsignal of an intermediate frequency band. The VSB modulator 7 provides afiltered (root-raised cosine) IF signal at a standard frequency (44 Mhzin the U.S.), with most of one sideband removed.

[0023] In particular, the eight level baseband signal is amplitudemodulated onto an intermediate frequency (IF) carrier. The modulationproduces a double sideband IF spectrum about the carrier frequency. Thetotal spectrum is too wide to be transmitted in the assigned 6 MHzchannel.

[0024] The sidelobes produced by the modulation are simply scaled copiesof the center spectrum, and the entire lower sideband is a mirror imageof the upper sideband. Therefore using a filter, the VSB modulatordiscards the entire lower sideband and all of the sidelobes in the uppersideband. The remaining signal (upper half of the center spectrum) isfurther eliminated in one-half by using the Nyquist filter. The Nyquistfilter is based on the Nyquist Theory, which summarizes that only a ½frequency bandwidth is required to transmit a digital signal at a givensampling rate.

[0025] Finally, there is a RF (Radio Frequency) converter 8 forconverting the signal of an intermediate frequency band from the VSBmodulator 7 into a signal of a RF band signal, and for transmitting thesignal to a reception system through an antenna 9.

[0026] The foregoing VSB communication system is at least partiallydescribed in U.S. Pat. Nos. 5,636,251, 5,629,958 and 5,600,677 by ZenithCo. which are incorporated herein by reference. The 8T-VSB transmissionsystem, which is employed as the standard digital TV broadcasting inNorth America and South Korea, was developed for the transmission ofMPEG video and audio data. As technologies for processing digitalsignals develop and the use of the Internet increases, the trendcurrently is to integrate digitized home appliances, the personalcomputer, and the Internet into one comprehensive system.

[0027] Therefore, in order to satisfy the variety of the demands ofusers, there is a need to develop a communication system thatfacilitates the addition and transmittal of a variety of supplementaldata to the video and audio data through the digital broadcastingchannel. It is predicted that the use of supplemental data broadcastingmay require PC (Personal Computer) cards or portable appliances, withsimple indoor antennas.

[0028] However, there can be a substantial reduction of signal strengthdue to walls and nearby moving bodies. There also can be ghost and noisecaused by reflective waves, which causes the performance of the signalof the supplemental data broadcasting to be substantially poor.Supplemental data broadcasting is different from general video and audiodata in that it requires a lower error ratio in transmission. Forgeneral video and audio data, errors imperceptible to the human eye orear are inconsequential. In contrast, for supplemental data, even onebit of error in the supplemental data (which may include programexecution files, stock information, and other similar information) maycause a serious problem. Therefore, the development of a communicationsystem that is more resistant to the ghost and noise occurring on thechannel is absolutely required.

[0029] In general, the supplemental data is transmitted by a timedivision system on a channel similar to the MPEG video and audio data.After the incorporation of digital broadcasting, there has already beena widespread emergence in the home appliance market of receiversequipped to receive ATSC VSB digital broadcast signals. These productsreceive MPEG video and audio data only. Therefore, it is required thatthe transmission of supplemental data on the same channel as the MPEGvideo and audio data has no adverse influence on the existing receiversthat are equipped to receive ATSC VSB digital broadcasting.

[0030] The above situation is defined as ATSC VSB backwardcompatibility, and the supplemental data broadcasting system must be asystem that is backward-compatible with the ATSC VSB communicationsystem.

SUMMARY OF THE INVENTION

[0031] Accordingly, the present invention is directed to a VSBcommunication system, and a signal format for the VSB communicationsystem that substantially obviates one or more of the problems due tothe limitations and disadvantages of the related art.

[0032] An object of the present invention is to provide an ATSC VSBtransmission system, which can transmit the present MPEG video and audiodata together with supplemental data.

[0033] Another object of the present invention is to provide an ATSC VSBtransmission system that is more robust to ghost and noise.

[0034] A further object of the present invention is to provide a newATSC VSB transmission system that is fully backward-compatible with arelated art ATSC VSB transmission system.

[0035] A still further object of the present invention is to provide atransmission data format that is suitable to an ATSC VSB transmissionsystem which is robust to ghost and noise.

[0036] Additional features and advantages of the invention will be setforth in the description that follows, and in part will be apparent fromthe description, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0037] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, theVSB transmitter for use with an MPEG data signal and a supplemental datasignal comprises a VSB supplemental data processor and a 8T-VSBtransmission system. The VSB supplemental data processor comprises aforward error correction coder that codes the supplemental data signal;repetition coder for inserting repetition bits to supplemental datasignal and outputting repetition data; a header inserter for inserting aheader to the supplemental data signal having the repetition datainserted therein; and a multiplexer for multiplexing the MPEG datasignal and the supplemental data signal having the header insertedthereto in at least one of a predetermined multiplexing ratio and unit.

[0038] The VSB transmission system is responsive to the VSB supplementaldata processor for modulating an output from the multiplexer to form atleast one data field comprising a plurality of segments that includes atleast one segment representing the supplemental data signal and at leastone segment representing the MPEG data signal.

[0039] According to one aspect of the present invention, the forwarderror correction coder is a Reed-Solomon coder. The supplemental datasignal includes at least one data packet having X bytes and theReed-Solomon coder provides parity bytes of Y bytes, wherein a total ofX and Y bytes is 184 bytes.

[0040] According to another aspect of the present invention, the headerinserter adds three bytes of header information to the data packet.Preferably ,a repetition coder repeatedly codes input 1 byte, convertsthe input 1 byte to 2 bytes, and outputs the resultant value. Thisimproves a receiving performance by widening the distance betweensymbols when a trellis coded modulator (TCM) performs coding. That is,the distance between symbols becomes wide by inputting 000, 110, 001,and 111 to the TCM with a repetition coding.

[0041] According to another aspect of the present invention, the VSBtransmitter further comprises an interleaver receiving data from theforward error correction coder and outputting to the repetition coder.The interleaver interleaves the supplemental data signal with forwarderror corrected code. Also said interleaver may omit the present of theinvention.

[0042] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0044]FIG. 1 illustrates a block diagram showing a conventional VSBtransmission system;

[0045]FIG. 2 illustrates a block diagram showing VSB signalconstellation

[0046]FIG. 3 illustrates a block diagram showing a VSB transmitter fortransmitting supplemental and MPEG data in accordance with a preferredembodiment of the present invention;

[0047]FIG. 4 illustrates the frame architecture of a transmission datafor a VSB transmission system in accordance with a preferred embodimentof the present invention;

[0048]FIG. 5 illustrates a diagram showing a process for multiplexingsupplemental data and MPEG data for forming a VSB data field;

[0049]FIG. 6 illustrates an example of inserting the repetition bitsinto the supplemental data by the repetition coder and generating apredefined data;

[0050]FIG. 7 illustrates a schematic diagram of a data interleaver forinterleaving supplemental data;

[0051]FIG. 8 illustrates a block diagram showing trellis coder andpre-coder

[0052]FIG. 9 illustrates an example of coding supplemental data(blocksize=164 byte); and

[0053]FIG. 10 illustrates another example of coding supplementaldata(block size=82 byte).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. FIG. 2 illustrates VSB signal constellation.

[0055]FIG. 3 illustrates a block diagram showing a VSB transmitter 110for the transmission of the supplemental and MPEG data in accordancewith a preferred embodiment of the present invention. FIG. 4 illustratesthe frame architecture of transmission data for a VSB transmissionsystem in accordance with a preferred embodiment of the presentinvention. FIG. 5 illustrates a diagram showing a process formultiplexing supplemental data and MPEG data for forming a VSB datafield. FIG. 6 illustrates a diagram showing a process for inserting anull sequence to generate a predefined sequence. FIG. 7 illustrates adiagram showing a data interleaver for interleaving supplemental data.FIG. 8 illustrates a block diagram showing trellis coder and pre-coder.

[0056]FIG. 9 illustrates a diagram showing an example of codingsupplemental data(block size=164 byte), and FIG. 10 illustrates adiagram showing another example of coding supplemental data(blocksize=82 byte).

[0057]FIG. 2 illustrates a constellation shape of a VSB signal accordingto the present invention. When additional data are repeatedlytransmitted, 4 symbols 000, 110, 001, and 111 are output. That is, oneof eight symbols 000, 001, 010, 011, 100, 101, 110, and 111 is generallyoutput when the TCM performs coding. In the present invention, one offour symbols is output. Therefore, the distance between symbols becomeswide, thereby reducing a rate of an error occurrence.

[0058] In FIG. 3, the VSB transmitter 110 in accordance with a preferredembodiment of the present invention includes a VSB supplemental dataprocessor 100 and a VSB transmission system 16. The description of theVSB transmission system 16 is described above in connection with FIG. 1,and thus, will not be repeated. According to the preferred embodiment ofthe present invention, the VSB supplemental data processor includes aReed-Solomon coder 11, a data interleaver 12, a null sequence inserter13, an MPEG header inserter 14, a multiplexer 15, an 8T-VSB transmissionsystem 16, and an antenna 17.

[0059] As shown in FIG. 3, for the transmission of the supplemental datafrom the VSB transmitter 110 (i.e., a broadcasting station) to a VSBreception system on a channel (terrestrial or cable), the VSBtransmitter 110 subjects the supplemental data to various digital signalprocesses. To provide backward compatibility of the present inventionwith existing devices, the supplemental data is preferably 164 bytepacket which will eventually be processed to be a 187 byte packet beforeentering the VSB transmission system 16. However, the size of thesupplemental data packet may be varied so long as the output of the VSBsupplemental data processor 100 is compatible with the VSB transmissionsystem 16.

[0060] In the VSB supplemental data processor 100, there is provided aReed-Solomon coder 11 for the correction of errors. The supplementaldata is coded at a Reed-Solomon coder (or R-S coder) 11. Preferably, theReed-Solomon coder 11 is used for subjecting the supplemental data toReed-Solomon coding and adding a 20 byte parity code to the output data.As described above, Reed Solomon encoding is a type of forward errorcorrection scheme applied to the incoming data stream. Forward errorcorrection is used to correct bit errors that occur during transmissiondue to signal fades, noise, etc. Various other types of error correctiontechniques known to one of ordinary skill in the art may be used as theforward error correction process.

[0061] According to the preferred embodiment, the Reed-Solomon coder 11of the VSB supplemental data processor takes 164 bytes of an incomingsupplemental data packet and mathematically manipulates them as a blockto create a digital sketch of the block contents. The 20 additionalbytes are added at the tail end of the original 164 byte packet. These20 bytes are known as Reed-Solomon parity bytes. Since Reed-Solomondecoders of the VSB reception system correct byte errors, and bytes canhave anywhere from 1 to 8 bit errors within them, a significant amountof error correction can be accomplished in the VSB receiver. The outputof the Reed-Solomon coder 11 is preferably 184 bytes (164 bytes from theoriginal packet plus 20 parity bytes).

[0062] The VSB supplemental data processor 100 further includes the datainterleaver 12, which interleaves the output data of the Reed-Solomoncoder 11. The interleaver 12 is for interleaving the coded supplementaldata to enhance performance against burst noise. The interleaver 12 maybe omitted, if necessary.

[0063] The data interleaver 12 according to the preferred embodimentmixes the sequential order of the supplemental data packet and dispersesor delays the supplemental data packet throughout time. The datainterleaver 12 then reassembles new data packets incorporating smallsections from many different supplemental data packets. Each one of thereassembled packets are 184 bytes long.

[0064] As described above, the purpose of the data interleaver 12 is toprevent losing of one or more packets due to noise or other harmfultransmission environment. By interleaving data into many differentpackets, even if one packet is completely lost, the original packet maybe recovered from information contained in other packets. However thereis a data interleaver in the ASTC 8T-VSB transmission system, the datainterleaver for the supplemental data can be omitted if it is notrequired to enhance the burst noise performance of the supplementaldata. For this reason, the data interleaver 12 may not be necessary forthe VSB supplemental data processor 100.

[0065] The VSB supplemental data processor 100 also includes therepetition coder 13 for inserting repetition bit to an allocated regionof the interleaved (if the data interleaver 12 was present) orReed-Solomon coded supplemental data for generating the predefinedsequence for the supplemental data at an input terminal of a Trelliscoder (shown in FIG. 8). The repetition data is inserted so that the VSBreception system receives the supplemental data more reliably, even in anoisy multipath fading channel. An example structure of the transmissiondata formed by the insertion of the repetition coder will be explainedbelow in detail with reference to FIG. 6.

[0066] Further referring to FIG. 3, the VSB supplemental data processor100 includes the MPEG header inserter 14 for adding an MPEG header tothe supplemental data having the repetition data inserted thereto, forbackward-compatibility with the legacy VSB reception system. Because theMPEG-II data supplied to the VSB transmission system 16 is 187 byteslong, the MPEG header inserter 14 places, preferably, three headers infront of each packet (which was 184 bytes) to form a 187 byte longpacket identical to the MPEG-II data packet.

[0067] The supplemental data having the MPEG header added thereto isprovided to a multiplexer 15. The multiplexer 15 receives as inputs theprocessed supplemental data from the MPEG header inserter 14 and MPEGdata packets. MPEG data packet, such as a broadcasting program (movie,sports, entertainment, or drama), coded through another path (outputfrom MPEG encoder), is received together with the supplemental data atthe multiplexer 15. Upon reception of the MPEG data and the supplementaldata, the multiplexer 15 multiplexes the supplemental data and the MPEGdata at a fixed ratio under the control of a controller defining amultiplexing ratio and unit and forwards the multiplexed data to the8T-VSB transmission system 16.

[0068] The 8T-VSB transmission system 16, which is described in detailin reference to FIG. 1, processes the multiplexed data and transmits theprocessed data to the VSB reception system through the antenna 17.

[0069] For example, the Reed-Solomon coder 11 uses a code having a blocksize N=184, a payload K=164, and an error correction capability T=10. Onthe other hand, as a generator polynomial of the Galois Field and theReed-Solomon coder 11, the same code as the the Reed-Solomon coder 2described with respect to FIG. 1 may be used. According to the preferredembodiment, other values of the block size N, the payload K, and theerror correction capability T may be used in the Reed-Solomon coder 11in FIG. 3. For an example, a code having N=184, K=154, and T=15 may beused, or a code having N=92, K=82, and T=5 may be used. Although theReed-Solomon code is used in the present invention, other code suitablefor error correction known to one of ordinary skill in the art may beused therein.

[0070]FIG. 4 illustrates the structure of a VSB data field used in theVSB transmission system 100. As shown in FIG. 4, one data field has 313segments: 312 data segments 124 and one field synchronizing segment 122.The 312 data segments have data segments of the supplemental data andthe MPEG data segments. Each data segment 124A has 184 byte data, a 3byte MPEG header, and the 20 byte ATSC Reed-Solomon parity. The 3 byteMPEG header will used by the MPEG decoder in the VSB reception system.

[0071] The use of the MPEG header is explained in more detail. ISO/IEC13818-1 has a definition on an MPEG transport packet header. If a 0×47synchronization byte is removed from the MPEG transport packet header, a3 byte header is left. A PID (program identification) is defined by this3 bytes. A transport part of the MPEG decoder discards a packet if thePID of the received packet received is not valid. For example, a nullpacket PID or other reserved PID can be used. Therefore, the MPEG headerinserter 14 in FIG. 3 inserts the 3 byte header containing such a PIDinto the supplemental data packet. Therefore, the supplemental data canbe discarded at the MPEG decoder of the legacy VSB receiver.

[0072]FIG. 5 illustrates a process for multiplexing the supplementaldata and the MPEG data at the multiplexer 15 in FIG. 3. As shown in FIG.5, the supplemental data is multiplexed with the MPEG data in segmentunits. The supplemental data is multiplexed with the MPEG data insynchronous to the field synchronizing signal used for synchronizing adata frame synchronization in the VSB transmission system.

[0073] Therefore, the VSB reception system determines the multiplexinglocations of the MPEG data and the supplemental data in the field datareceived synchronous to the field synchronizing signal. The VSBreception system demultiplexes the MPEG data and the supplemental databased on the multiplexing locations. A multiplexing ratio and method formultiplexing the MPEG data and the supplemental data may vary withamounts of data thereof.

[0074] Information on the variable multiplexing method and ratio may beloaded on, for example, a reserved area of the 92 bits not used in thefield synchronizing signal. By retrieving and decoding such information,the VSB reception system identifies the correct multiplexing ratio andmethod from the multiplexing information contained in the fieldsynchronizing signal.

[0075] Alternatively, the multiplexing information may be inserted, notonly in the reserved area of the field synchronizing signal, but also inthe data segment of the supplemental data. As shown in FIG. 5, of theentire 312 multiplexed data segments, one half are occupied by the datasegments representing the supplemental data inputted to the VSBsupplemental data processor 100. One of the supplement data segment maybe used to transmit the multiplexing information for use by the VSBreception system.

[0076]FIG. 6 illustrates an example of inserting the repetition bit intothe supplemental data by the repetition coder 13 according to thepreferred embodiment of the present invention. The supplemental datahaving the repetition data inserted therein is transmitted to the VSBreception system.

[0077] When 1 byte is input, a repetition bit is inserted as shown tooutput 2 bytes. As shown in FIG., the repeatedly coded additional dataare coded to a leed solomon, interleaved, and input (d1 and d0) to theTMC without passing through a randomizer within 8T-VSB transmittingsystem. Hereinafter, a relation between the repeatedly coded additionaldata and the TMC will be explained with reference to FIG. 8.

[0078] The VSB transmitter 110 of the present invention is required tohave identical probabilities of occurrence of the 8 levels, for havingbackward-compatibility with the related art VSB transmission system.Therefore, the presence of the 0's and 1's in the sequence received asthe input signal D0 at the Trellis coder are required to be almost thesame.

[0079]FIG. 7 illustrates a block diagram of the data interleaver 12 forinterleaving the supplemental data in FIG. 3. According to the preferredembodiment, a convolutional interleaver may be used as the datainterleaver 12. However, other suitable interleaver, such as a blockinterleaver, known to one of ordinary skill in the art may also be used.

[0080] Referring to FIG. 7, the data interleaver 12 has ‘B’ ( preferably46) branches, and ‘M’ (preferably 4) bytes of unit memory. The datainterleaver 12 may be operative synchronous to a field synchronizationsignal of the VSB transmission system 16. The ‘B’ branches, and the ‘M’bytes of unit memory of the data interleaver 12 may be changed to othersuitable value without deviating from the gist of the present invention.

[0081] Because the VSB transmission system 16 already includes a datainterleaver 3, as shown in FIG. 1, the data interleaver 12 in the VSBsupplemental data processor 1100 of FIG. 2 may be omitted if no furtherburst noise performance improvement is required.

[0082]FIG. 8 illustrates a trellis coder and pre-coder. In FIG. 8, if 2bits (d1 and d0) are input, 3 bits (c2, c1, and c0) are output and thenconverted to one of 8 levels in 8 VSB converter. Also, the additionaldata are input to the TMC without passing through the pre-coder. Sincethe output of an interleaver shown in FIG. 7 is a byte unit and isdivided into 4 units (two bits per unit) per one byte and then input tothe TMC. At this time, the input bits d0 and d1 are output as c1 and c2as they are. Bits of the additional data are the same as d0 and d1 asthe additional data passed through the repetition coder. Accordingly,the output of the TMC is represented as one of 4 symbols shown in FIG.2. Also, the receiver detects the repeatedly coded data in advance.Therefore, by using this information, a performance of a slicerpredictor used in a channel equalizer can be improved and trellisdecoding performance can also be improved.

[0083]FIG. 9 illustrates a block diagram showing an example ofsupplemental data coding according to the preferred embodiment of thepresent invention. Referring to FIG. 9, the supplemental data has ablock size of 164 bytes. FIG. 9 illustrates the process of coding thesupplemental data packet until the supplemental data packet is providedto the multiplexer 15. This occurs after the supplemental data packetpasses the Reed-Solomon coder 11, the data interleaver 12, therepetition coder 13, and the MPEG header inserter 14 in FIG. 3 insuccession.

[0084] The operation of the VSB supplemental data processor 100according to the present invention will be described. According to FIG.9, a Reed-Solomon 20 byte parity is inserted to the supplemental datathat is 164 bytes long by the Reed-Solomon coder 11. This processchanges the supplemental data into a 184 byte packet. A number of paritybytes may vary with a number of the supplemental data bytes. Forexample,, if the supplemental data has 154 bytes, the parity has 30bytes. At the end, the number of the supplemental data bytes having theparity bytes added thereto is fixed to be 184 bytes in advance. Thesupplemental data having the parity added thereto is interleaved by thedata interleaver 12 and provided to the null sequence inserter 13 92bytes by 92 bytes. The null sequence inserter 13 inserts 92 bytes of thenull data into each of the 92 bytes of supplemental data to provide two184 byte packets for the 184 bytes of supplemental data, where the 20parity bytes are included in only one of the two 184 byte packets.

[0085] Thereafter, the MPEG header inserter 14 inserts 3 bytes of MPEGheader, preferably containing the PID, to the front part of each of thesupplemental data packets for backward-compatibility with the relatedart ASTC 8T-VSB transmission system. The multiplexer 15 multiplexes eachof the supplemental data packets from the MPEG header inserter 14 andthe MPEG data received through another route, and transmits themultiplexed data to the VSB transmission system 16. The VSB transmissionsystem 16 codes the multiplexed data and transmits the data to the VSBreception system.

[0086]FIG. 10 illustrates a diagram showing another example of codingthe supplemental data. Referring to FIG. 10, 10 bytes of parity bits areinserted into the 82 extra bytes by the Reed-Solomon coder 11, to changethe extra bytes into a 92 byte packet. The number of parity bytes varieswith the number of the supplemental data bytes. That is, if thesupplemental data has 72 bytes, then the parity has 20 bytes. At theend, the supplemental data having the parity added thereto is fixed tohave 92 bytes in advance. The 92 bytes of supplemental data having the10 bytes of parity added thereto is interleaved by the interleaver 12,and provided to the null sequence inserter 13, and the repetition coder13 inserts 92 bytes of null sequence into the 92 bytes of supplementaldata, to provide a total 184 bytes of packet. Accordingly, each of the184 bytes of packets includes 10 parity bytes.

[0087] Similar to FIG. 9, the MPEG header inserter 14 inserts 3 bytes ofMPEG header to the front part of the 184 bytes of supplemental datapackets for backward-compatibility with the related art ASTC 8T-VSBtransmission system, for a total of 187 bytes of data. Finally, themultiplexer 15 multiplexes each of the supplemental data packets fromthe MPEG header inserter 14 and MPEG data received through anotherroute, and transmits the multiplexed data to the VSB transmission system16. The VSB transmission system 16 codes the multiplexed data, andtransmits the data to the VSB reception system. At the end, FIGS. 9 and10 are identical in that the total number of bytes of the supplementaldata having the repetition coder inserted thereto is 184, and the totalnumber of bytes of the supplemental data having the MPEG header addedthereto is 187.

[0088] As has been explained, the present invention has the followingadvantages. First, supplemental data can be transmitted on the samechannel with MPEG data with the supplemental data multiplexed with theMPEG data.

[0089] Second, a backward-compatibility with the conventional ATSC 8TVSB system can be sustained. That is, the reception of the MPEGtransport data at the ASTC 8T-VSB receiver is not affected. Third,reliable reception both of the MPEG data and the supplemental data atthe reception system is facilitated by using the predefined sequenceinserted in the supplemental data even on a channel with excessiveghost. Fourth, a noise immunity of the supplemental data is enhanced atthe VSB reception system by using the predefined sequence inserted inthe supplemental data. Fifth, transmission of other MPEG data throughsupplemental data path is permitted, which in turn permits reception ofthe MPEG data even in a poor channel state.

[0090] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the VSB communicationsystem, and the signal format for the VSB communication system of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A VSB transmitter for use with an MPEG data signal and a supplemental data signal, the VSB transmitter comprising: a VSB supplemental data processor comprising: a forward error correction coder that codes the supplemental data signal; a repetition coder for inserting a repetition bit to the supplemental data signal subjected to the forward error correction coder for generating a predefined sequence; a header inserter for inserting a header to the supplemental data signal having the repetition bits inserted therein; and a multiplexer for multiplexing the MPEG data signal and the supplemental data signal having the header inserted thereto in at least one of a predetermined multiplexing ratio and unit; and a VSB transmission system connected to the VSB supplemental data processor for modulating an output from the multiplexer to form at least one data field comprising a plurality of segments that includes at least one segment formed from the supplemental data signal and at least one segment formed from the MPEG data signal.
 2. The VSB transmitter of claim 1, wherein the forward error correction coder is a Reed-Solomon coder.
 3. The VSB transmitter of claim 2, wherein the supplemental data signal includes at least one data packet having X bytes and the Reed-Solomon coder provides parity bytes of Y bytes, wherein a total of X and Y bytes is 184 bytes.
 4. The VSB transmitter of claim 3, wherein the header inserter adds three bytes of header information to the data packet, wherein the header information contains program identification.
 5. The VSB transmitter of claim 3, wherein the repetition coder converting Input “1” byte to output “2” byte and outputting said converted byte, to MPEG header inserter.
 6. The VSB transmitter of claim 5, wherein the output byte has substantially the same occurrence of the number of input bits.
 7. The VSB transmitter of claim 1, further comprising an interleaver receiving data from the forward error correction coder and outputting to the repetition coder, the interleaver interleaves the supplemental data signal coded by forward error correction code.
 8. The VSB transmitter of claim 7, wherein the forward error correction coder is a Reed-Solomon coder.
 9. The VSB transmitter of claim 8, wherein the supplemental data signal includes at least one data packet having X bytes and the Reed-Solomon coder provides parity bytes of Y bytes, wherein a total of X and Y bytes is 184 bytes.
 10. The VSB transmitter of claim 9, wherein the header inserter adds three bytes of header information to the data packet, wherein the header information contains program identification.
 11. The VSB transmitter of claim 1, wherein the repetition coder divides the one data packet of the supplemental data signal into a plurality of data packets.
 12. The VSB transmitter of claim 11, wherein the divieded repetition data has substantially the same occurrence of input bits and output bit.
 13. The VSB transmitter of claim 1, wherein the multiplexing unit is a segment, and the multiplexing ratio varies with amounts of MPEG data packets representing the MPEG data signal and supplemental data packets representing the supplemental data signal.
 14. The VSB transmitter of claim 13, wherein the multiplexing ratio of the supplemental data packets and the MPEG data packets in the multiplexer is one segment to one segment.
 15. The VSB transmitter of claim 13, wherein the multiplexing ratio of the supplemental data packets and the MPEG data packets in the multiplexer is one segment to three segments.
 16. The VSB transmitter of claim 1, wherein the multiplexer is responsive to a field synchronizing signal used for synchronizing a data frame of the VSB transmission system.
 17. The VSB transmitter of claim 1, wherein the data field has 312 data segments and one field synchronizing segment.
 18. A VSB supplemental data processor for use with a VSB transmission system to provide a supplemental data signal and an MPEG data signal thereto, wherein the VSB transmission system modulates at least one data field comprising a plurality of segments that includes at least one segment formed from the supplemental data signal and at least one segment formed from the MPEG data signal, the VSB supplemental data processor comprising: a forward error correction coder that codes the supplemental data signal; a repetition coder for inserting a repetition bit to the supplemental data signal subjected to the forward error correction coder for generating a predefined sequence; a header inserter for inserting a header to the supplemental data signal having the null sequence inserted therein; and a multiplexer for multiplexing the MPEG data signal and the supplemental data signal having the header inserted thereto in at least one of a predetermined multiplexing ratio and unit.
 19. The VSB supplemental data processor of claim 18, wherein the forward error correction coder is a Reed-Solomon coder.
 20. The VSB supplemental data processor of claim 19, wherein the supplemental data signal includes at least one data packet having X bytes and the Reed-Solomon coder provides parity bytes of Y bytes, wherein a total of X and Y bytes is 184 bytes.
 21. The VSB supplemental data processor of claim 20, wherein the header inserter adds three bytes of header information to the data packet, wherein the header information contains program identification.
 22. The VSB transmitter of claim 1, wherein the repetition coder divides the one data packet of the supplemental data signal into a plurality of data packets.
 23. The VSB transmitter of claim 12, wherein the divieded repetition data has substantially the same occurrence of input bits and output bit.
 24. The VSB supplemental data processor of claim 18, further comprising an interleaver receiving data from the forward error correction coder and outputting to the null sequence inserter, the interleaver interleaves the supplemental data signal with forward error corrected code.
 25. The VSB supplemental data processor of claim 24, wherein the forward error correction coder is a Reed-Solomon coder.
 26. The VSB supplemental data processor of claim 25, wherein the supplemental data signal includes at least one data packet having X bytes and the Reed-Solomon coder provides parity bytes of Y bytes, wherein a total of X and Y bytes is 184 bytes.
 27. The VSB supplemental data processor of claim 26, wherein the header inserter adds three bytes of header information to the data packet, wherein the header information contains program identification.
 28. The VSB supplemental data processor of claim 26, wherein the repetition coder divides the one data packet of the supplemental data signal into a plurality of data packets.
 29. The VSB transmitter of claim 28, wherein the divieded repetition data has substantially the same occurrence of input bits and output bit.
 30. The VSB supplemental data processor of claim 18, wherein the multiplexing unit is a segment, and the multiplexing ratio varies with amounts of MPEG data packets representing the MPEG data signal and supplemental data packets representing the supplemental data signal.
 31. The VSB supplemental data processor of claim 30, wherein the multiplexing ratio of the supplemental data packets and the MPEG data packets in the multiplexer is one segment to one segment.
 32. The VSB supplemental data processor of claim 30, wherein the multiplexing ratio of the supplemental data packets and the MPEG data packets in the multiplexer is one segment to three segments.
 33. A method for a supplemental data packet and an MPEG data packet in a VSB transmitter comprising a VSB supplemental data processor and a VSB transmission system, the method comprising the steps of: subjecting the supplemental data packet of preset bytes to a Reed-Solomon coding and adding a Reed-Solomon parity data of preset bytes to the supplemental data packet; interleaving the coded supplemental data packet; inserting repetition data into the interleaved supplemental data packet for producing at least one supplemental data packet of a preset number of bytes; adding an MPEG header of preset bytes to each one of the supplemental data packets; multiplexing the MPEG data packet with the supplemental data packet at a preset multiplexing ratio; and modulating the data multiplexed at the preset multiplexing ratio through the VSB transmission system.
 34. The method claim 33, wherein the Reed-Solomon parity is included to only one of the supplemental data packets.
 35. The method of claim 33, wherein the inserting repetition data includes the steps of; dividing the supplemental data packet into two supplemental data packets having the same numbers of bytes; and inserting a repetition data having the same bytes with the supplemental data packet into each one of the supplemental data packets to provide two supplemental data packets each having the repetition data inserted therein.
 36. The method of claim 35, wherein each one of the supplemental data packets has 184 bytes comprising 92 bytes of supplemental data 92 bytes of the repetition data.
 37. The method of claim 33, wherein the MPEG header is an identification code for identifying whether the multiplexed data is the supplemental data packet or the MPEG data packet.
 38. A VSB signal format comprising: an MPEG header region 3 bytes; and a supplemental data region having original supplemental data and repetition data data and having 184 bytes.
 39. The VSB signal format of claim 38, wherein the supplemental data region further includes a Reed-Solomon parity of preset bytes. 